1. Field of the Invention
The invention relates to a method and an apparatus for reducing power loss in devices for contactless data and energy transfer, having a stationary part and a moveable part, with at least one coil in each part for data and energy transfer, and at least one memory unit in the moveable part.
2. Description of the Related Art
Such an apparatus is disclosed in German Patent DE 34 47 560 C2, corresponding to U.S. Pat. No. 4,697,183, and in particular in FIGS. 1 and 2 thereof and the associated text describing those figures.
Those patents shows a device for contactless data and energy transfer, including a stationary part called a microstation and an oscillator for contactless power transfer with the aid of at least one pair of coils in a moveable part called a microunit. In the device described therein, two coils are provided in the stationary part, which form a total of two pairs of coils with two coils in the moveable part. Data transfer from the moveable part to the stationary part is effected by simultaneously varying the load on the two coils of the moveable part, which assures that there will be evidence of the load variation at one of the two coils of the stationary part, even if the pairs of coils were transposed. The oscillation of the oscillator in the stationary part is split into two separate oscillations (a reference oscillation and an information oscillation). Upon one oscillation (the information oscillation), a phase displacement relative to the other oscillation is imposed as a function of the data to be transferred, with the reference oscillation serving as a reference variable. The phase-displaced oscillation is supplied to the moveable part through one of the pairs of coils, and the other oscillation is supplied through the other pair of coils. The power is transferred through both pairs of coils, with the aid of both oscillations. In the moveable part, the transferred oscillations are supplied to a demodulator in the form of a phase comparator, which recovers the data from the phase displacement.
A respective rectifier is connected to the output side of each connection terminal of each coil in the moveable part. The output that furnishes the positive voltage in one of the rectifiers is interconnected with the output that furnishes the positive voltage in the other of the rectifiers, and the two output terminals of the two rectifiers, both of which furnish the negative voltage, are connected to one another as well. The common output of the two rectifier circuits is connected to a voltage regulator for furnishing the operating voltage of the moveable part. The voltage regulator may be a serial or a parallel regulator, for example.
Published European Application No. 0 466 949 A1, corresponding to U.S. application Ser. No. 07/590,033, filed Sep. 28, 1990 now abandoned, shows a device for contactless data and energy transfer and is distinguished from the known device described above primarily due to the fact that the power transfer is accomplished with the aid of only one pair of coils, and that the data transfer from the moveable part to the stationary part is effected by varying the load on the coil of the moveable part, which coil is not used for the power transfer.
That device for contactless data and energy transfer, as illustrated in FIG. 2 thereof, is provided with a first unit in the stationary part ST formed with an oscillator OSC and a first transistor T1. The first unit is provided for energy transfer by means of a first coil L1a. A second unit formed with an EXOR gate, a second transistor T2 and an evaluation circuit AS for data transfer from the stationary part to the moveable part by means of a second coil L1b. The second unit has a data input DT1 and a data output DR1 which can be connected to a non-illustrated process control unit, for instance a microprocessor.
The moveable part BT has two coils L2a and L2b which, together with the coils L1a and L1b of the stationary part, form two pairs of coils. The two coils L2a and L2b of the moveable part are each followed by a rectifier circuit GRa and GRb, respectively. The two rectifiers are each followed by a modulator Moda and Modb and by a voltage regulator SRA and SRB, respectively. Furthermore, the outputs of the coils L2a and L2b are connected with a demodulator Demod. The demodulator, the voltage regulators and the modulators can be connected to a non-illustrated logic circuit, for instance a microprocessor. The rectifiers, the modulators, the voltage regulators, the demodulator and the logic circuit together form a function unit.
In order to assure that the coils of the stationary part can be arbitrarily associated with the coils of the moveable part to form pairs of coils, and thus to assure that energy or data can be transferred through each of the two coils, even if not simultaneously, not only a rectifier circuit but also at least the final control element of a voltage regulator along with at least one switch, which can vary the load on the pair of coils associated with it as a function of its triggering and of the switch position effected by its triggering, are associated with each of the two coils of the moveable part. It is also possible for a voltage regulator and a variable load to be assigned to each coil, or for only one voltage regulator and one variable load, which can be selectively connected to the output side by reversing the coils of the moveable part, to be provided. In all such cases, a logical linkage must assure that the amplitude modulator required for data transfer from the moveable part to the stationary part always varies the load of the pair of coils which does not participate in the energy transfer, and which has a voltage regulator or voltage regulator final control element which is consequently not activated, or which does not have the voltage regulator connected to its output side.
If the coils of the moveable part and the coils of the stationary part can be coupled arbitrarily and a demodulator circuit as described above having a circuit for fixing the logic level of the signal is therefore provided, then in the same way in which it defines the logic level, the circuit unit can also recognize at which of the coils of the moveable part the information oscillation, which is variable in its phase position relative to the reference oscillation, is transferred. In such a device for contactless data and energy transfer, a logical linkage acts as a function of a demodulator circuit containing the information to define which coil of the moveable part is used for the data transfer from the moveable part to the stationary part, and which coil is intended for the energy transfer. It is also assured that the data transfer from the moveable part to the stationary part is performed with the aid of whichever coil of the moveable part is not being used for energy transfer at that moment. In order to assure a continuous energy supply to the moveable part, the coil that transfers the reference oscillation has a voltage regulator connected to its output side, or a voltage regulator connected to the output side of that coil is activated. For the data transfer from the moveable part to the stationary part, the load is varied as a function of the data to be transferred, at the coil of the moveable part that transfers the information oscillation.
One of the main problems of the above-described devices for contactless data and energy transfer is the manufacturing tolerances of the various components, and the resultant varying operating conditions in different systems. Such pronounced tolerances affect the data of the coil pairs (such as the coupling factor) above all, but they also affect the supply of energy to the primary side and the energy systems on the secondary side as well. Such tolerances have to be compensated for by supplying additional energy to the primary side. The excess energy is converted into heat on the secondary side in a so-called shunt controller. The usually poor heat conduction coefficients of the moveable parts (such as a chip card or key) cause impermissibly severe heating of those parts, which can destroy the component contained in the moveable part in the worst case.
It is accordingly an object of the invention to provide a method for reducing power loss in devices for contactless data and energy transfer and an apparatus for performing the method, which overcome the hereinafore-mentioned disadvantages of the heretofore-known methods and devices of this general type and which reduce the excess energy in the moveable part to a minimum.